MHC antigens or transplantation antigens, which in man are also called HLA antigens, play an essential part in T cell activation and the concomitant immune response. Thus e.g. protein antigens are dependent on interactions with MHC antigens for presentation to and activation of T cells during a normal immune response. Likewise, MHC dependent presentation of autoantigens are of key importance in T cell dependent autoimmune processes.
A certain type of MHC antigens, i.e. the so called MHC class II antigens are expressed by a variety of normal cells either constitutionally or after activation (1). Among tumor cells, malignancies of the haematopoietic system commonly express MHC class II molecules. Although MHC class II antigens are not restricted to tumor cells, they may constitute an attractive target for therapy since most normal cells would be spared.
A potent agent capable of eliminating MHC class II antigen expressing cells may therefore be useful both for interruption of autoimmune processes and for the destruction of certain malignant cells.